1. Field of the Invention
This invention relates to optical recording mediums and more particularly, to a method for making an optical recording medium which comprises as a recording layer a monomolecular film or a monomolecular built-up film having polydiacetylene bonds exhibiting photochromic characteristics.
2. Description of the Prior Art
As is known in the art, polymers of diacetylene derivatives have one dimensional main chain with .pi.-electron conjugated bonds in the molecule and thus exhibit electric conductivity and a non-linear optical effect. These polymers have been widely studied for use as a light or electron-responsive material.
As a process of preparing polydiacetylene, there is known a process wherein crystals of a diacetylene compound (G. Wegner, Z. Nature forsch 246(1989) 824) or a monomolecular built-up film of a diacetylene compound formed by the Langmuir-Blodgett method (C. Bubeck et al., Der Bunsenges Phys. Chem. 86,495 (1982)) is polymerized by irradiation of a radiation.
However, it has not been reported yet that a single crystal of polydiacetylene having a large area is obtained. On the other hand, a thin film with a large area is obtained from a monomolecular built-up film of a diacetylene compound formed by the LB method, but the production efficiency is very poor. If such a thin film is applied as an optical recording medium, production costs become very high with little industrial utility.
It is known that when using linear hydrocarbon derivatives having --Si--Cl group at one end, a monomolecular film can be very readily formed on the surface of a hydrophilic substrate by chemical adsorption in organic solvent. The addition of a certain substituent to the surface of the monomolecular film will render the surface hydrophilic by chemical reaction after the adsorption. This is known to be effective in obtaining a monomolecular built-up film as described, for example, in U.S. Pat. No. 4,535,061, to J. Sagiv.
Accordingly, if a substance having a diacetylene bond in part of a linear hydrocarbon is subjected to chemical adsorption, a monomolecular film of the diacetylene derivative can be formed having a layer thickness in the order of several ten angstroms. A multi-layered built-up film can also be obtained readily.